As well known to those skilled in the art, waste water may contain a wide variety of undesirable components which may restrict its use or disposal by passage to natural bodies of water. Illustrative of industrial waters which may normally be discharged into adjoining bodies of water is the aqueous discharge from an oil production platform. These platforms are constructed in fresh water lakes or more commonly in salt water bodies in which drilling is carried out and in due course production of hydrocarbons. Prior to further treatment of the hydrocarbons it is necessary to separate them from the produced water which may be passed to waste.
Produced water contains a wide variety of components depending upon the details of operation. It may contain dissolved water-soluble salts typified by those present in sea water, which commonly contains the following:
TABLE ______________________________________ Element Parts per Million (w) ______________________________________ Cl 18,980 Na 10,561 Mg 1,272 S 884 Ca 400 K 380 Br 65 C (inorg) 28 Sr 13 (SiO.sub.2) 0.01-7.0 B 4.6 Si 0.02-4.0 C (org) 1.2-3.0 Al 0.16-1.9 F 1.4 ______________________________________
Many other elements may be present in amounts each less than about 1 ppm. See Handbook of Chemistry and Physics (44 Ed) 1962, Page 3488.
Commonly sea water is considered as being a dilute (3.5 w %) solution of sodium chloride.
In typical production platforms, as the hydrocarbon is recovered from the undersea sources, there is recovered a substantial portion of produced water including formation water and injected water. Formation water is that water which is naturally present in the oil or gas reservoir. This may amount to as little as less than 1 v % at the beginning of production but typically increases during the life of the well. Injected water is typically sea water which has been injected into the well to enhance the recovery of hydrocarbon (See for example Somerville et al Environmental Effect of Produced Water from North Sea Oil Operations Marine Pollution Bulletin Vol. 18, No 10, pp 549-558 (1987) (Great Britain).
Produced water commonly is found to contain immiscible hydrocarbons, typified by crude petroleum, in amounts of 20-80, say 50 w %; and it may contain, in suspension, insoluble inorganic solids, typically in amounts up to say 0.5 w %, typically 0.01-0.5, say 0.1 w %.
The produced water may also contain 20-40 mg/l of dissolved hydrocarbons including benzene, toluene, and xylene.
A principal undesired component of produced water may be dissolved water-soluble organic electrolytes (WSOE). Produced waters, as found for example in the North Sea or in the Gulf of Mexico, may contain as much as up to about 1 w % WSOE; and commonly they may be found in amount of 30-500 wppm as wppm as measured by the Freon Extraction Oil and Grease Test (ASTM Test method 413.2) and thereafter determining the intensity of the IR carboxylate band.
Upon analysis, the water-soluble organic electrolytes may be found to include: fatty acids, typified by C.sub.1 -C.sub.8 acids such as acetic, propionic, butyric, benzoic, etc. typically as their salts; as well as other anion-forming compounds typified by phenols.
The pH of the produced water is typically below 7 and commonly it is found to be 4-7. A common Gulf of Mexico produced water may be found to have a pH of about 6.
Produced water may contain, as water-soluble organic electrolytes (WSOE), non-hydrocarbon organic matter, largely as salts of lower aliphatic carboxylic acids such as acetic, propionic, butyric acids, commonly in amounts up to about one gram per liter.
The produced water may also contain 20-40 mg/l of dissolved hydrocarbons including benzene, toluene, and xylene. This produced water is accompanied by immiscible hydrocarbons, typified by crude petroleum in amounts up to 0.w %; and it may also contain in suspension, insoluble solids, typically in amount up to say 0.w %.
Other aqueous media which may be treated by the process of this invention include various waste waters from industrial sources. For background on the problems generated by these liquids and some attempts to solve those problems, the following may be noted:
(i) European patent 251,691 to the Water Research Commission, Transvaal, South Africa as assignee of Buckley et al published January 7, 1988;
(ii) Simpson et al The Effect of pH on the Nanofiltration of the Carbonate System in Solution, Desalination 1 64 (1987) pp 305-319;
(iii) Bindoff et al The Nanofiltration and Reuse of Effluent from the Caustic Extraction Stage of Wood Pulping, Desalination 67 (1987) pp 455-465;
(iv) Mickley A Charged Ultrafiltration Membrane Process for Water Softening IDA Journal 1 (1) (1985) March, pp 1-14;
(v) Koros et al Polymeric Membrane Materials for Solution Diffusion Based Permeation Separations (private Communication);
(vi) Somerville et al Environmental Effect of Produced Water from North Sea Oil Operations. Marine Pollution Bull., 18 (10) (1987) p 549-558;
(vii) C. S. Fang et al Air Stripping for Treatment of Produced Water J. Petroleum Technology May (1968) p 619-624;
(viii) P. Eriksson Nanofiltration Extends the Range of Membrane Filtration Environmental Progress 7 (1) (1988);
(ix) K. J. Keda et al New Composite Charged Reverse Osmosis Membrane Desalination 68 (1988) 109-119.
No completely economically satisfactory solution to the problem has been found--particularly as it relates to the treatment of produced water on offshore drilling platforms--to yield a water of sufficient purity so that it meets governmental discharge limits applicable to water which is discharged into the sea.
Prior attempts to clean produced water have included the use of settling and/or skimming basins; but these have not proven to be economically desirable because inter alia they are unable to remove solubilized organics. Other technologies such as carbon adsorption have not proven to be economically desirable because they are characterized by size and weight which are undesirably high when measured against the limitations of e.g. an offshore drilling platform.
Processes utilizing reverse osmosis membranes have not been found to be satisfactory because their productivity is extremely low due inter alia to their high rejection of salts such as sodium chloride--which create an undesirably high osmotic pressure across the membrane.
Prior art attempts to solve the problem have not satisfactorily yielded a technique which has been found to satisfactorily remove water-soluble organic electrolytes from the aqueous waters.
It is an object of this invention to provide a novel process for treating an aqueous charge liquid to attain a product containing a lesser amount of water-soluble organic electrolytes. Other objects will be apparent to those skilled in the art.